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In Reply
- Vishal Uppal, John Kinsella (16 April 2009)
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Unsatisfactory performance of supraglottic airway devices
- John J Henderson (1 April 2009)
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Vishal Uppal Glasgow Royal Infirmary, John Kinsella
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Editor – We thank Dr Henderson for his comments on our paper.1 We completely agree with him on the fact that supraglottic airway devices (SADs) have an important role in anaesthesia and there will be a small proportion of patients with an inadequate seal. We would like to clarify that although we had a significant leak in two of the 20 study patients, there was no evidence of any airway obstruction and we were able to maintain end tidal CO2 with-in the normal range for these two patients during pressure-controlled ventilation (PCV). There are various studies comparing work of breathing between SADs and the tracheal tubes. Initial in-vitro study found that the laryngeal mask airways (LMAs) imposed less resistance and required lower additional inspiratory work compared with the corresponding sized tracheal tubes.2 An in-vivo study in spontaneously breathing subjects shows same results.3 However for controlled ventilation some studies suggest the total inspiratory resistance is lower for the LMA4,5 and others suggest that it is similar to that of a tracheal tube.6,7 When we compared expired tidal volumes (ETV) between the i-gel and the tracheal tube, the median ETV was always larger for the i-gel group during PCV. This suggests that the resistance offered by the i-gel is lower than that offered by the corresponding sized tracheal tube. We also agree to Dr Henderson on the issue of a greater variability in performance of SADs when compared with the tracheal tubes. In our opinion this should not be equated to unsatisfactory performance as there are several well established advantages of using SADs when compared with the tracheal tube (discussed in our paper).1 The reason for this variability is a fundamental difference in mechanism of seal with upper respiratory tract. On inflation of the cuff, the tracheal tubes form a tube-within- tube seal with the trachea whereas the cuff of SADs forms an end-to-end seal with pharynx. The end-to end seal of SAD depends mainly on how well the shape of cuff of SAD matches the shape of the pharynx. There is good evidence to suggest that oxygenation is similar for the LMA and tracheal tube during spontaneous and positive pressure ventilation, but better for the LMA during emergence.3, 8-9 Failure rate for SADs is 1- 2%, this includes failure to insert the SAD into the pharynx, failure to produce clear airway and failure to form an effective seal.10-11 The incidence of laryngospasm with the use of SADs is about 1.5% but the incidence of severe laryngospasm is much lower 0.07%.10-11 The overall incidence of laryngospasm appears to be similar to the pre-SAD studies.12 Bronchospasm can be triggered by tracheal tubes but does not occur with the use of SADs in normal adults.13 Negative pressure pulmonary oedema is a well known complication associated with acute airway obstruction in spontaneously breathing patients. It is rare with the use of SADs (<10,000) and is associated with malposition, laryngospasm, displacement, and tube occlusion through biting.11 On the basis of this evidence and our data, we stand by our assertion that the i-gel can be used as a reasonable alternative to the tracheal tube during PCV with moderate airway pressures. V. Uppal* J. Kinsella Glasgow, UK *E-mail: drvishal76@rediffmail.com References 1. Uppal V, Fletcher G, Kinsella J. Comparison of the i-gel with the cuffed tracheal tube during pressure-controlled ventilation. Br J Anaesth 2009; 102: 264-8. 2. Bhatt SB, Kendall AP, Lin ES, Oh TE. Resistance and additional inspiratory work imposed by the laryngeal mask airway. A comparison with tracheal tubes. Anaesthesia 1992; 47: 343-7 3. Joshi GP, Morrison SG, White PF, Miciotto CJ, Hsia CC. Work of breathing in anesthetized patients: laryngeal mask airway versus tracheal tube. J Clin Anesth 1998; 10: 268-71. 4. Fassoulaki A, Paraskeva A, Karabinis G, Melemeni A. Ventilatory adequacy and respiratory mechanics with laryngeal mask versus tracheal intubation during positive pressure ventilation. Acta Anaesthesiol Belg 1999; 50: 113-7. 5. Berry A, Brimacombe J, Keller C, Verghese C. Pulmonary airway resistance with the endotracheal tube versus laryngeal mask airway in paralyzed anesthetized adult patients. Anesthesiology 1999; 90: 395-7. 6. Boisson-Bertrand D, Hannhart B, Rousselot JM, Duvivier C, Quilici N, Peslin R. Comparative effects of laryngeal mask and tracheal tube on total respiratory resistance in anaesthetised patients. Anaesthesia 1994; 49: 846-9 7. Reissmann H, Pothmann W, Füllekrug B, Dietz R, Schulte am Esch J. Resistance of laryngeal mask airway and tracheal tube in mechanically ventilated patients. Br J Anaesth 2000; 85: 410-6. 8. Fröhlich D, Schwall B, Funk W, Hobbhahn J. Laryngeal mask airway and uncuffed tracheal tubes are equally effective for low flow or closed system anaesthesia in children. Br J Anaesth 1997; 79: 289-92. 9. Webster AC, Morley-Forster PK, Dain S, et al. Anaesthesia for adenotonsillectomy: a comparison between tracheal intubation and the armoured laryngeal mask airway. Can J Anaesth 1993; 40: 1171–7. 10. Verghese C, Brimacombe JR. Survey of laryngeal mask airway usage in 11,910 patients: safety and efficacy for conventional and nonconventional usage. Anesth Analg 1996; 82: 129-33. 11. Brimacombe J. Laryngeal Mask Anesthesia. Principles and Practice, 2nd edn. London, UK: WB Saunders, 2004; 115, 118, 551-552 12. Olsson GL, Hallen B. Laryngospasm during anaesthesia. A computer-aided incidence study in 136,929 patients. Acta Anaesthesiol Scand 1984; 28: 567 -75. 13. Kim ES, Bishop MJ. Endotracheal intubation, but not laryngeal mask airway insertion, produces reversible bronchoconstriction. Anesthesiology 1999; 90: 391-4. Conflict of Interest:None declared |
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John J Henderson Gartnavel General Hospital, Glasgow
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Editor - In the abstract of their recent paper, Uppal et al 1 suggest that the i-gel SAD (supraglottic airway device) can be used as a reasonable alternative to the tracheal tube during pressure-controlled ventilation with moderate airway pressure. They compared leak volumes and fractions measured with the i-gel and cuffed tracheal tube during pressure -controlled ventilation. They found no “statistically significant” differences. However their data showed very large leak volumes and fractions in 2 of the 20 (10%) patients, demonstrating very unsatisfactory performance in these patients. Airway obstruction could contribute to these leaks. Others have published data which shows great variation in the performance of SADs. Work of breathing (WOB) was compared between the face mask, LMA and tracheal tube during spontaneous ventilation in anaesthetised children 2. WOB was computed from a flowmeter and oesophageal pressure. WOB was significantly lower with the tracheal tube than the other airways. However a very striking finding was the great variation in WOB in the LMA group. In some patients the WOB was less than the mean value for the tracheal tube, but in many it was very much higher. In another study, airflow resistance was compared between the LMA and tracheal tube in mechanically ventilated patients 3. Resistance was calculated from proximal and distal pressures and airflow. In 12 patients the mean airflow resistance imposed by the LMA and larynx was similar to that imposed by the tracheal tube. However the airflow resistance was markedly increased in 3 patients in the LMA group. The importance of these studies is that reporting of complete results demonstrates the great variability in performance of supraglottic airway devices (SADs). In particular, SADs provide a less reliable airway than a properly placed tracheal tube. This reduced reliability is probably a consequence of malposition due to blind insertion and variable glottic obstruction. This scientific evidence of variable and unsatisfactory performance may seem to conflict with the many clinical reports on SAD use which describe a “satisfactory” airway and good outcome. However, closed claims analyses reveal deaths associated with SAD use 4 and there have certainly been unreported cases. Airway obstruction during SAD use may cause delayed hypoxaemia due to negative pressure pulmonary oedema 5, as well as immediate hypoxaemia. Airway obstruction during SAD use may be a consequence of several mechanisms. Obstruction caused by glottic compression 6 may be less frequent (as demonstrated by higher sealing pressure) when cuff pressure is limited to 60 cm H2O 7, but this pressure control will not affect obstruction caused by undiagnosed laryngeal lesions 8, impaction in the glottis or vocal cord closure 9. Laryngospasm is associated with the use of SADs 10. Airway obstruction following insertion of SADs is often improved by manipulation of the SAD. However serious obstruction can develop during surgery and is particularly dangerous as the need for emergency intraoperative tracheal intubation exposes the patient to an increased risk of hypoxaemia and probably airway trauma as the intubation may be performed in the badly-positioned hypoxaemic patient. Some quote very low incidences of intraoperative conversion to tracheal intubation, but figures of 2% during tubal ligation 11 and 13% of obese patients during laparoscopic cholecystectomy 12 have been reported. SADs have an important role in anaesthesia and perform well in most patients. However there is good scientific evidence that in a significant proportion of patients they perform very badly in comparison with tracheal tubes. Their performance should always be assessed meticulously (capnography and expired tidal volume are recommended by LMA Inc.), and preferably documented, after insertion. When there is evidence of airway obstruction immediately after insertion they should be replaced with a face-mask or tracheal tube if repositioning or replacement of the SAD fail to achieve an excellent airway. The anaesthetist should have a plan for management of intra-operative airway obstruction during SAD use. Airway management should be designed to minimise risks and based on all the scientific evidence. J. J. Henderson Gartnavel General Hospital Glasgow G12 0YN, UK john@airway.org.uk References 1. Uppal V, Fletcher G, Kinsella J. Comparison of the i-gel with the cuffed tracheal tube during pressure-controlled ventilation. Br J Anaesth 2009; 102: 264-8. 2. Keidan I, Fine GF, Kagawa T, Schneck FX, Motoyama EK. Work of breathing during spontaneous ventilation in anesthetized children: a comparative study among the face mask, laryngeal mask airway and endotracheal tube. Anesth Analg 2000; 91: 1381-8. 3. Reissmann H, Pothmann W, Fullekrug B, Dietz R, Schulte am EJ. Resistance of laryngeal mask airway and tracheal tube in mechanically ventilated patients. Br.J Anaesth 2000; 85: 410-6. 4. Peterson GN, Domino KB, Caplan RA, Posner KL, Lee LA, Cheney FW. Management of the difficult airway: a closed claims analysis. Anesthesiology 2005; 103: 33-9. 5. Sullivan M. Unilateral negative pressure pulmonary edema during anesthesia with a laryngeal mask airway. Can.J Anaesth 1999; 46: 1053-6. 6. Brimacombe J, Richardson C, Keller C, Donald S. Mechanical closure of the vocal cords with the LMA ProSeal. Br J Anaesth 2002; 89: 936. 7. Brimacombe J, Keller C, Morris R, Mecklem D. A comparison of the disposable versus the reusable laryngeal mask airway in paralyzed adult patients. Anesth Analg 1998; 87: 921-4. 8. Kariya N, Nishi S, Minami W et al. Airway problems related to laryngeal mask airway use associated with an undiagnosed epiglottic cyst. Anaesth Intensive Care 2004; 32: 268-70. 9. van Zundert A, Brimacombe J, Al-Shaikh B, Mortier E. Utility of fiberoptic assessment in the differential diagnosis of glottic impaction versus reflex glottic closure with the laryngeal mask airway. Anesthesiology 2005; 103: 671-2. 10. Flick RP, Wilder RT, Pieper SF et al. Risk factors for laryngospasm in children during general anesthesia. Paediatr Anaesth 2008; 18: 289-96. 11. Evans NR, Skowno JJ, Bennett PJ, James MF, Dyer RA. A prospective observational study of the use of the Proseal laryngeal mask airway for postpartum tubal ligation. Int J Obstet Anesth 2005; 14: 90-5. 12. Maltby JR, Beriault MT, Watson NC, Liepert D, Fick GH. The LMA- ProSeal is an effective alternative to tracheal intubation for laparoscopic cholecystectomy. Can J Anaesth 2002; 49: 857-62. Conflict of Interest:None declared |
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